Transparent films

ABSTRACT

The invention relates to an optically transparent polymer film or extrudate product made of a polymer composition comprising a semi-crystalline polyamide having a melting temperature of at least 270° C. or a blend of the semi-crystalline polyamide (A) and a second polymer (B), and optionally at least one additive, wherein the semi-crystalline polyamide (A) is present in an amount of more than 50 wt. %, relative to the total weight of the polymer composition, the polymer composition in the optically transparent polymer film or extrudate product has a melting temperature (Tm-C) in the range of 270-340 ° C., and wherein the film or a part of the extrudate product has a haze of less than 12% and a light transmittance, of at least 88% measured with the method according to ASTM D1003A.

The present invention relates to optically transparent polymer films andother optically transparent extruded products. More particular, thepresent invention relates to such products made of a polyamidecomposition that are both transparent and have good mechanical andthermal properties, more particular high heat resistance. The inventionalso relates to high temperature resistant polymer film materials thatare used as substrate material for inorganic deposition with the aim ofachieving ultra-high barrier flexible film materials.

Heat resistant transparent sheets and films are being explored forpossible use in electronic devices, such as displays, as a replacementfor conventional glass substrates, in order to improve flexibility andproduce thinner, more lightweight products. These films must have highthermal deformation temperatures of more than 250° C.: i.e. higher thanfor conventional acrylic or polycarbonate sheets. Currently usedmaterials for high temperature film applications include polyethylenenaphthalate (PEN), polyarylate (PAR), polyethersulfon (PES),polyamideimide (PAI), polyimide (PI), polyetherimide (PEI) andpolynorbornene (PNB). Due to their high melting temperature or glasstransition temperature films made of these materials keep their shapeand mechanical properties up to relatively high temperatures and do notmelt or degrade unless heated to very high temperature. Recently, highheat durable transparent polyimide films, with a thickness of up to 0.25mm, a light transmittance of 90% and capable of enduring temperatures ofup to 280° C., were developed by Mitsubishi. However, most of thesematerials are expensive and difficult to process.

Polyamide resins have excellent toughness, strength, and chemicalresistance, which make them useful as engineering resins for a widevariety of applications. For many applications it would be desirable touse a transparent polyamide, but many polyamides are semi-crystallinematerials, and, as such, are often opaque as incident light is scatteredby the crystalline domains present in the polymers. Transparentpolyamides are known, but are typically amorphous, or blends ofamorphous thermoplastic aliphatic copolyamides with limited amounts ofsemicrystalline thermoplastic polyamides, or semicrystallinethermoplastic polyamides with low melting point and relative lowcrystallization speed, and as a result, have reduced heat resistance andarticles formed from these materials tend to suffer from creeping ordeformation over time.

U.S. patent application US2006/0030692A1 describes products with atransparency of at least 80%. In one example 88% transparency ismentioned. These products are based on microcrystalline copolyamideswith a crystallinity of 10-30% comprising at least 50 wt. % of monomerswith at least 9 C atoms. The products have a glass transitiontemperature of 40-90° C. and melting temperature of 150-200° C.

U.S. Pat. No. 4,404,317 discloses blends of amorphous thermoplasticaliphatic polyamides copolymers with semicrystalline thermoplasticpolyamides. The resulting blends could be made transparent and aredisclosed to have good solvent resistance, dimensional stability, andretention of physical properties under moist or wet conditions. Japanesepatent application publication 03-033157 discloses a polyamide resincomposition with improved alcohol resistance prepared by compounding acopolyamide obtained from isophthalic acid, terephthalic acid,hexamethylenediamine and an alicyclic diamine, with a semiaromaticpolyamide obtained from an aromatic diamine and a dicarboxylic acid.

U.S. patent application US2006/036044-A1 discloses a blend of 50-95 wt.% of an amorphous semi-aromatic polyamide and 5-50 wt. % of asemi-crystalline semi-aromatic polyamide having a melting temperature atleast 280° C. These compositions have a light transmittance of as low as65% or more. In one example, for which a light transmittance of 89% wasreported, the composition comprised 18 wt. % of the semi-crystallinesemi-aromatic polyamide and 82 wt. % of an amorphous semi-aromaticpolyamide.

Thus there is a need for high temperature resistant polymer filmmaterials, in particular for better performing materials compared to theamorphous polyamides and/or cheaper materials like the polyimides.

It is an object of the present invention to provide a polyamide polymerfilm that is both transparent and has good mechanical properties andretention thereof at elevated temperature as well as a high heatresistance, exhibited by dimensional stability with limited thermalexpansion and/or high deformation temperatures. Another object of thepresent invention is to provide polyamide polymer films that have bothtransparency and improved barrier properties.

The invention disclosed and claimed herein concerns a transparentpolymer film or an extrudate product made of a polymer compositioncomprising a semi-crystalline polyamide (A) wherein the semi-crystallinepolyamide (A) has a melting temperature (Tm-A) of at least 270° C. andis present in an amount of respectively at least 60 wt. % in case thesemi-crystalline polyamide (A) consists of a semi-aromaticsemi-crystalline polyamide or of a blend of a semi-aromaticsemi-crystalline polyamide and an aliphatic semi-crystalline polyamide,or at least 75 wt. % in case the semi-crystalline polyamide (A) consistsof an aliphatic semi-crystalline polyamide, wherein the wt. % isrelative to the total weight of the polymer composition, the polymercomposition has a melting temperature (Tm-C) of at least 270° C., andthe film or a part of the extrudate product has a haze of less than 12%and a light transmittance of at least 88%, measured with the methodaccording to ASTM D1003A.

The term semi-crystalline polyamide used further herein will be meant toinclude both semi-aromatic semi-crystalline polyamide and aliphaticsemi-crystalline polyamide, unless specifically expressed otherwise.

With an optically transparent product is further herein understood, ifnot specified otherwise, a product comprising an integral part having alight transmittance of at least 88%, measured according to ASTM D1003A.With the light transmittance is understood the percentage of theluminous flux transmitted through a specimen compared to the luminousflux incident upon it. The haze is the percentage of transmitted lightpassing through a specimen by forward scattering, which deviates fromthe incident light by no more than 2.5°. The optical properties aremeasured on the film as such, or on the thin part in the extrudateproduct, without correction for the thicknesses.

Further herein the term optically transparent and transparent may beused next to each other but will have the same meaning, i.e. opticallytransparent, unless clearly stated otherwise.

A film is herein understood to have the regular meaning of a productwith a flat shape that is generally indicated with the word film orsheet. Whereas the word films and sheets might be used elsewhere todiscriminate for example between thinner and thicker products, orbetween semi-endless products and products with limited length,respectively, the word film is herein understood to cover all of these.Semi-endless thin films may easily take the form of a long roll film,while sheets with limited length may be stacked into piles.

With the term extrudate product is herein understood a product obtainedby an extrusion process, but that is not a film or a sheet. Whereas afilm or sheet will typically extend in two dimensions, apart form itsthickness, the extrudate product is herein understood to differ from afilm or sheet in that it extends in three dimensions. For example, theextrudate product may be a tube or a profile.

The part of the extrudate product having a haze of less than 12% and alight transmittance of at least 88% will herein also be denoted astransparent part.

With the term melting temperature is herein understood the meltingtemperature, measured with the method according to ASTM D3418-03 by DSCin the second heating run with a heating rate of 10° C./min. Herein themaximum peak of the melting endotherm is taken as the meltingtemperature.

The melting temperature Tm-A of the semi-crystalline polyamide (A)mentioned herein is determined on the polymer, whereas the meltingtemperature Tm-C of the composition is measured on the composition inthe film or extrudate product.

With a semi-crystalline polymer is herein understood a polymer having amelting enthalpy of at least 5 J/g. In line with that an amorphouspolymer is herein understood to be a polymer having a melting enthalpyof less than 5 J/g.

With the term melting enthalpy is herein understood the exothermicenergy, measured with the method according to ASTM D3418-03 by DSC inthe second heating run with a heating rate of 10° C./min.

With the term glass transition temperature (Tg) used herein isunderstood the temperature, measured with the method according to ASTM E1356-91 by DSC in the second heating run with a heating rate of 10°C./min, falling in the glass transition range and showing the highestglass transition rate. The temperature showing the highest glasstransition rate is determined as the temperature at the peak of thefirst derivative (with respect of time) of the parent thermal curvecorresponding with the inflection point of the parent thermal curve.

The polymer composition in the transparent polymer film and extrudateproduct according to the invention may comprise next to thesemi-crystalline polyamide with the said high melting point one or moreother polymers and/or one or more additives. A requirement is howeverthat the resulting polymer composition has a melting temperature (Tm-C)of at least 270° C. Preferably Tm-C is in the range of 270-340° C., morepreferably in the range of 280-330° C., or even better 290-320° C. Thehigher the melting temperature, the better the high heat resistance is.On the other hand, in general the lower the melting temperature, theeasier the processing is.

The melting temperature Tm-A of the semi-crystalline polyamide (A),being at least 270° C., may vary over a wide range and may be as high asor even higher than 340° C. This latter will depend on the thermalstability of the semi-crystalline polyamide (A) and the compoundingpossibilities thereof. The processing will be improved when such a highmelting polymeide is blended with another lower melting semi-crystallineor amorphous polyamide. Preferably, the semi-crystalline polyamide has aTm-A in the range of 270-340° C.

The polymer composition, or the semi-crystalline polyamide (A) therein,has a melting enthalpy, which may vary over a large range.

In a preferred embodiment of the invention, the polymer composition, orthe semi-crystalline polyamide (A) therein, has a melting enthalpy, ofat least 25 J/g, more preferably at least 40 J/g, and still morepreferably at least 50 J/g. In line with the present invention themelting enthalpy shall be primarily related to the melting point of thesemi-crystalline polyamide (A), and consequently shall be within, orclose to the temperature range of 270-340° C. Preferably, at least 50%,more preferably at least 75% of the measured melting enthalpy shall bewithin the temperature range of 270-340° C.

The higher the crystallinity of the transparent product, the better theheat resistance and dimensional stability at elevated temperatures,better mechanical properties, and lower thermal expansion. Especiallyafter stretching and/or heat setting of the film or annealing of theextrudate product the melt enthalpy may increase and may attain valueswell above 70 J/g, and even as high as 90 J/g and higher, possiblyattain values >90 J/g, while still having a transparent polyamide.Though the films may have a melt enthalpy as high as 120 J/g or higher,very good properties are already obtained when the melting enthalpy isin the range of 25-100 J/g.

The semi-crystalline polyamide (A) may be any semi-crystalline polyamidehaving a melting temperature of at least 270° C. and preferably is inthe range of 270-340° C. Suitably said semi-crystalline polyamide is asemi-crystalline semi-aromatic polyamide, or a semi-crystallinealiphatic polyamide or a combination, or any blend thereof. In case thesemi-crystalline polyamide (A) consists of a blend of differentsemi-crystalline polyamides, the melting temperature of the blend shallstill be at least 270° C., and preferably be in the range of 270-340° C.

The semi-crystalline aliphatic polyamide can be for examplepolytetramethylene adipamide (PA46), or a copolyamide of PA46, forexample a copolyamide of PA46 and PA6 or PA66, or a copolyamide of PA66and PA6CHDA, wherein CHDA represents units derived from1,4-cyclohexanedicarboxylic acid.

The semi-crystalline semi-aromatic polyamide can be a polyamide withrepeat units derived from dicarboxylic acids and diamines wherein eitherthe dicarboxylic acids, or the diamines, or both, comprises aromaticcomponents while the remainder comprises aliphatic dicarboxylic acidsand/or diamines, which can be linear, branched, or cyclic, and/orarylaliphatic dicarboxylic acids and diamines.

Examples of suitable aromatic dicarboxylic acids are terephthalic acidand isophthalic acid.

Preferably, the semi-crystalline semi-aromatic polyamide comprisesrepeat units derived from terephthalic acid as the dicarboxylic acids.Examples of suitable aromatic diamines are meta-xylylene diamine andpara-xylylene diamine.

Examples of suitable semi-crystalline semi-aromatic polyamides includehomopolyamides like PA7T, PA9T, PA10T and PA12T having a meltingtemperature in the range of 270-350° C., and copolyamides of PA4T, PA5T,PA6T and/or PA8T, with for example PA7T, PA9T, PA10T, PA 11T PA12T, PA6,PA66, and/or PMXD6. The homopolymers of PA4T, PA5T, PA6T and PA8T have amelting temperature above 340° C., but the copolymers can be formulatedsuch as to have a melting temperature below 340° C. Suitablecopolyamides include PA10T/6T, PA9T/M8T (wherein M8=2-Methyloctamethylene diamine), PA6T/5T, PA6T/M5T (wherein M5=2-Methylpentamethylene diamine), and PA6T/10T. The polyamides may comprise otherrepeat units of other diamines and diacids, next to those mentioned inthe copolyamides hereabove, thus forming more complex copolyamides. Forfurther examples of suitable semi-crystalline semi-aromatic copolyamidessee Kunststoff Handbuch, (Carl Hanser Verlag 1998) Band ¾ Polyamidechapter 6.

Preferably, the semi-crystalline semi-aromatic polyamide has a meltingtemperature in the range of 290-335° C., more preferably in the range of310-330° C. With a higher minimum melting temperature the film hasbetter thermal and dimensional properties. With a lower maximum meltingtemperature the polymer composition can be more easily processed intothe transparent film or the extrudate product. A higher meltingtemperature can be accomplished e.g. by using a higher amount ofterephthalic acid and/or alicyclic or aromatic diamines, or short chainlinear aliphatic diamines. The person skilled in the art can adapt themelting point using common general knowledge and routine experiments.

In one embodiment of the transparent film, respectively the extrudateproduct according to the invention, the semi-crystalline polyamide (A)is a semi-crystalline semi-aromatic copolyamide (A-X) consisting ofrepeat units derived from:

-   -   (a) 25-45 mole % terephthalic acid,    -   (b) 5-25 mole % of an aromatic dicarboxylic acid different from        terephthalic acid, and/or an aliphatic dicarboxylic acid    -   (c) 5-30 mole % of an diamine chosen from the group consisting        of ethylene diamine, trimethylene diamine, tetramethylene        diamine and pentamethylene diamine    -   (d) 20-45% of a diamine comprising at least 6 C-atoms, and        optionally    -   (e) 0-10 mole % of one or more aminocarboxylic acids and or        lactams, and    -   (f) 0-3 mole % of compounds being mono-functional or        tri-functional in amino and/or carboxylic acid groups;        wherein the mole % of each of a-f is relative to the total of        a-f.

The components a-f are preferably present, either individually, or incombination with each other, in the following amounts: (a) 35-45 mole %;(b) 5-15 mole %; (c) 10-25 mole %; (d) 15-25 mole %; (e) 0-5 mole %; and(f) 0-1 mole %, wherein the mole % of each of a-f is relative to thetotal of a-f.

It has been found that a transparent film or extrudate product accordingto this embodiment can be easily produced, using film take-up conditionsthat are typically applied for preparing transparent PA6 films. Ofcourse the temperature of the melt in the extruder has to be adoptedbecause of the higher melting point of the semi-crystalline polyamideA-X. Even when the said semi-crystalline polyamide had a meltingtemperature as high as 325° C., and was used without a second polymer, atransparent film was obtained. The transparency was also retained afterheating of the film despite crystallization induced by and occurringupon said heating.

In this respect it is noted that applying the same conditions for thepreparation of films from PA6T/66 polyamide with a melting temperatureof about 320° C. did not result in a transparent film but resulted inquite hazy films instead.

Preferably, in the said embodiment the semi-crystalline polyamide (A)has a melting temperature (Tm-A) in the range of 290-335° C., morepreferably in the range of 310-330° C. A higher melting temperature canbe accomplished e.g. by using a higher amount of component (a) and orcomponent (c) in the semi-crystalline semi- aromatic copolyamide in theabove embodiment.

In another embodiment of the transparent film or extrudate productaccording to the invention, the semi-crystalline polyamide (A) comprisespolytetramethylene adipamide (PA46) or a copolyamide of PA46, PA46consists of repeat units derived form tetramethylene diamine and adipicacid. Copolyamides of PA46 comprise (i) repeat units derived formtetramethylene diamine and adipic acid and (ii) repeat units derivedfrom other diacids, diamines and/or amino carboxylic acids and/orlactams. In line with the present invention the copolyamide must have amelting temperature of at least 270° C., and better in the range270-340° C. Preferably, the repeat units (i) derived from tetramethyleneadipamide are present in an amount of at least 75 wt. %, preferably atleast 90 wt. %, relative to the total weight of the copolyamide. Thehigher the content of the repeat units (i) the better the thermalproperties and dimensional stability of the transparent film,respectively the extrudate product.

Polyamide films of PA46 copolyamides are known. However, these are allhazy translucent films. This is generally believed to be due to the fastcrystallization speed of PA46, which has been considered to beinhibitive for making transparent films of PA46 at all. The inventorshave confirmed that with standard film preparation processes as well aswith a film preparation process wherein the extruded film wasimmediately quenched in a cold quenching liquid, shortly after beingtaken up by a pick-up roll. Films thus obtained were hazy and showedseveral irregularities and white spots. The inventors have succeeded inpreparing transparent PA46 films by applying a film extrusion processwherein a chilling role was positioned very close to the slit die of theextrusion equipment and cooled with ice water.

The transparent PA46 films thus obtained remained transparent uponlonger annealing of the film at elevated temperature. The films showed ahigh level of crystallinity as exhibited by a high melting enthalpy inDSC measurements. In contrast to the films made of semi-aromaticsemi-crystalline polyamides, the PA46 films did not show any sign ofpost crystallization in said DSC measurements. This might be interpretedin that the transparent PA46 films were already crystallized. Despitethat the films were highly transparent.

The transparent PA46 films obtained from the above extrusion processcould also be biaxially stretched to high stretching levels withoutdamaging or rupture of the film. This in contrast with the hazy PA46films described above that were more difficult to draw and showed pinholing and other defects already early in the stretching process.

The optically transparent polymer film, as well as the extrudate productaccording to the invention, comprising the semi-crystalline polyamide(A) with the high melting point as the major compound, has the advantageof very good thermal stability and dimensional stability. Thetransparent polymer film also has a low permeability for oxygen (O₂) andcarbon dioxide (CO₂).

The use of a second polymer (B) in the polymer composition in thepresent invention is in particular advantageous in combination with thehigher melting semi-crystalline polyamide, thereby easing the processingof the semi-crystalline polyamide at melt temperatures above the meltingtemperature for making the transparent film or product according to theinvention.

The second polymer (B) may still be present in relatively large amountsto achieve films with improved properties. The amounts of the secondpolymer that can be used depend on the nature of the semi-crystallinepolyamide (A) and the second polymer (B), being either bothsemi-crystalline or the first one semi-crystalline, and the otheramorphous, the melting temperature of the semi-crystalline polymers andthe compatibility between the two polymers.

In particular in combination with a higher melting semi-crystallinepolyamide, for example with a Tm-A in the range of 300-340° C., theamount of the second polymer (B) may be larger, while still retaining afilm or extrudate product with a high heat resistance.

In combination with a somewhat lower melting semi-crystalline polyamide(A), for example with a Tm-A in the range of 280-300° C., the amountthat can be used but can still be substantial, meanwhile retaining themelting temperature Tm-C of the polymer composition in the in the rangeof 270-340° C. With a semi-crystalline polyamide (A) with a Tm-A in therange of 270-280° C., the presence of a second polymer will be criticalfor the melting temperature Tm-C of the polymer composition, and theamount thereof is preferably very low if not absent at all.

Preferably, the amount of the second polymer is limited therebyobtaining even better mechanical and thermal properties. The betterproperties can be in better creep resistance, higher mechanicalstrength, and better dimensional stability at elevated temperatureand/or under humid conditions. With a lower amount of the secondpolymer, the film also shows a lower O₂ and/or CO₂ permeability.

Suitably, the second polymer is present in an amount of 1-40 wt. % or,more strictly 10-25 wt. %. Preferred amounts for the second polymer, ifany, are in the range of 0-25 wt. % and even better 0-10 wt. % Hereinthe weight percentage, as throughout this specification, are relative tothe total weight of the polymer composition, unless expressly notedotherwise.

In case of the presence of an aliphatic semi-crystalline polyamide, thesecond polymer has to be limited to 25 wt. % anyway.

The second polymer (B) may suitably comprise an amorphous semi-aromaticpolyamide and/or a semi-crystalline aliphatic or semi-aromatic polyamidehaving a melting temperature below 270° C. The second polymer (B) beingsuch an amorphous or low melting semi-crystalline polyamide has theadvantage of being well compatible with the semi-crystalline polyamide(A), leading to higher transparency and lower haze values.

Such amorphous or lower melting semi-crystalline polyamides may wellhave an O₂ and/or CO₂ permeability that is higher than that of thesemi-crystalline polyamide (A). It has been observed that with a contentof 25 wt. % or less of the second polymer (B) even when having such ahigher O₂ and/or CO₂ permeability, the low O₂ and/or CO₂ permeability ofthe semi-crystalline polyamide (A) in the transparent film is hardlyaffected.

An example of such a lower melting semi-crystalline polyamide that cansuitably be used in the present invention is polyamide-6.

The polymer composition in the film or extrudate product according tothe invention optionally comprises, next to the semi-crystallinepolyamide (A) or the blend thereof with the second polymer (B), one ormore additives. The additive, or additives, can be any auxiliaryadditive used in transparent films, provided the individual amounts andcombinations are chosen such that the transparency is not jeopardized,at least not in significant extent. These additives may be chosen fromthe group consisting of plasticizers, stabilizers, dyes, opticalbrighteners, coloring agents, lubricants, nanoscale filler andstrengthening materials, and preferably comprises heat stabilizersand/or nanoscale fillers. Types and amounts of additives can be selectedby the skilled person by common general knowledge and routinemeasurement. Suitably, the additive, or additives, are present in anamount in the range of 0.01-20 wt. %, preferably 0.1-10 wt. %, 0.25-5wt. %. Herein the wt. % are relative to the total weight of thecomposition.

The polymer composition in the film or extrudate product according tothe invention may well consists of:

-   -   (A) 60-100 wt. % of the semi-crystalline semi-aromatic polyamide        having a Tm-A in the range of 270-340° C.,    -   (B) 0-40 wt. % of the second polymer, and    -   (C) 0-10 wt. % of at least one additive,        wherein the wt. % are relative to the total weight of the        polymer composition.

It is noted that the amounts of A, B and C can vary within the saidranges, meanwhile they are linked to each other in the sense that thecombined amount of A, B, and C is 100%.

Preferably the polymer composition consists of:

-   -   (A) 75-99.75 wt. % of the semi-crystalline polyamide having a        Tm-A in the range of 270-340 ° C.,    -   (B) 0-25 wt. % of the second polymer, and    -   (C) 0.25-10 wt. % of at least one additive,        wherein the wt. % are relative to the total weight of the        polymer composition.

In a particular embodiment the polymer composition consists of

-   -   (A) 85-99.5 wt. % of the semi-crystalline polyamide having a        Tm-A in the range of 270-340° C.,    -   (B) 0-14.5 wt. % of a second polymer, and    -   (C) 0.5-5 wt. % of at least one additive,        wherein the wt. % are relative to the total weight of the        polymer composition.

The film or according to the invention, as well as the thin transparentpart in the extrudate product according to the invention, may have athickness varying over a broad range, while still having sufficienttransparency. The range will depend on the type of semi-crystallinepolyamide as well as on the process conditions applied. Withsemi-crystalline semi-aromatic copolyamides like the polyamide (A-X)described above the thickness may be as high as 500 μm or even higher,while still having good transparency properties. The thickness may be aslow as 1 μm or lower. Preferably the thickness is in the range of 1-200μm. With polyamide 46 as the main component in the polymer composition,the thickness of the film or of the thin transparent part of theextrudate product will generally be lower, and suitably the thickness isin the preferred range of 1-200 μm.

In general the more preferred thickness is in the range of 5-150 μm, oreven 10-100 μm, or still more preferred 20-60 μm.

The film, as well as the thin transparent part in the extrudate productaccording to the invention also preferably has a haze of less than 5%,more preferably less than 2%, and/or a light transmittance of at least90%, more preferably more than 92%, when measured according to ASTMD1003A.

The invention also relates to a process for preparing a transparentpolymer film as according to the invention. The process according to theinvention comprises steps wherein

-   -   (1) a polymer composition comprising a semi-crystalline        polyamide (A) having a melting temperature (Tm-A) of at least        270° C. as described hereabove is heated and melt extruded        through a slit die to form an extruded polymer layer;    -   (2) the extruded polymer layer is led over a chilling role        having a temperature below 40° C., thereby forming a polymer        film, and    -   (3) the polymer film is collected,        wherein the polymer film has a haze of less than 12% and a light        transmittance of at least 88% when measured according to ASTM        D1003A.

Preferably, the slit die and the chilling role are separated from eachother by a distance of at most 2 cm, more preferably 1.5 cm, and thechilling role has a surface temperature of at most 10° C., morepreferably at most 8° C. In a preferred embodiment of the process, thedistance is at most 1.3 cm and the chilling role has a surfacetemperature of at most 5° C. More preferably the chilling role has a wetsurface and is cooled with ice water. This provides a better contactbetween the extruded polymer layer and the chill role and an even bettercooling of the polymer film. This latter embodiment is advantageouslyapplied for preparing transparent PA46 films with relative largethickness. To achieve an even better contact between the chilling roleand the extruded polymer layer, pinning techniques, like electrostaticpinning and air pinning may be applied.

The invention also relates to a process for after-treatment of a polymerfilm. In said process the transparent polymer film according to theinvention or obtained by the process described hereabove, is subjectedto a drawing step wherein the film is stretched, or a heat setting or anannealing step, wherein the transparent polymer film, having a glasstransition temperature (Tg-C) and a melting temperature (Tm-C), isheated to and/or kept for a certain period, at a temperature betweenTg-C and Tm-C.

Since the film obtained by the process may be an amorphous film, whichshows an induced crystallization upon heat treatment, and the film onlyshows a melting temperature after the heat treatment, the meltingtemperature (Tm-C) referred above relates to the melting temperaturemeasured on the film after the after-treatment. The person skilled inthe art will be able to determine the melting temperature by DSCmeasurements and adjust the temperature applied during theafter-treatment process accordingly.

The process for preparing the transparent polymer film and the processfor after-treatment of the polymer film may be carried out separately orbe combined in one consecutive process. The effects of the drawing step,the heat setting step and the annealing step are increased mechanicalproperties and reduced water uptake.

The invention also relates to a stretched transparent film, obtainablewith the said process.

The invention also relates to a process for preparing an extrudateproduct comprising a transparent part. The process comprises stepswherein

-   -   i. a polymer composition of as described above is heated and        melt extruded through a die;    -   ii. the extruded polymer composition is led through a quenching        liquid having a temperature below 40° C., thereby forming a        solid product, and    -   iii. the solid product is collected,        wherein the solid product comprises a part having a haze of less        than 12% and a light transmittance of at least 88% when measured        according to ASTM D1003A.

In a preferred embodiment, the temperature of the quenching liquid isbelow 20° C., more preferably below 10° C.

The invention also relates to the use of the transparent polymer filmaccording to the invention described above, or obtainable by a processdescribed below, as well as to particular embodiment of the extrudateproduct according to the invention described above.

The extrudate product according to the invention may well be asteam-sterilizable medical article, such as a container or a syringe,etc.

The transparent polymer film according to invention can be used for manyapplications, such as for barrier films and in electronic applications.

The barrier films can advantageously be applied in mono- andmultilayered packaging materials.

The films may be used for electrical and electronic applications.Examples include the use of the films as PCB carrier etc., inelectrodes, sensors, photovoltaic cells and other optical devices,display components, more particular as back plane for flat paneldisplays and flexible displays, such as LCD and OLEDs, includingelectronic paper and organic EL displays.

The transparent polymer film according to the invention is eminentlysuited for use as a substrate material for inorganic deposition,resulting in ultra-high barrier performance. The inorganic depositionmay optionally be structured. Suitably, the inorganic deposit is anindium-tin-oxide (ITO) or a copper cladding. These make these filmsuseful for ITO, a-Si TFT and Low temperature polysilicone TFT (LTPS).

The invention is further illustrated with the following Examples andComparative Experiments.

Materials

-   PA-1 Polyamide 46, aliphatic polyamide, Tm 295° C., Tg 80° C.,    VN=230 ml/g-   PA-2 Polyamide 46/6, aliphatic copolyamide, 7 wt. % caprolactam, Tm    285° C., Tg 78° C., VN 215 ml/g-   PA-3 Polyamide 6T/4T/66, semi aromatic copolyamide, Tm 325C, Tg 125°    C., RV 1.9-   PA-4 Polyamide 6T/66, semi aromatic copolyamide, Tm 320° C., Tg 100°    C., RV 2.6-   PA-5 Polyamide 6, aliphatic polyamide, Tm 220° C., Tg 51° C., RV=3.2

Each of the polyamides comprised around 0.5-1.0 wt. % of a standardadditive package comprising processing aids and heat stabilizers.Melting temperature (Tm), glass transition temperature (Tg), andrelative viscosity (RV) mentioned herein were measured by the methodsdescribed below.

Methods Viscoity: Relative Viscosity (RV), Viscosity Number (VN)

The measurement of the relative viscosity (RV) was performed accordingto ISO 307, fourth edition. For the measurement a pre-dried polymersample was used, the drying of which was performed under high vacuum(i.e. less than 50 mbar) at 80° C. during 24 hrs. Determination of therelative viscosity was done at a concentration of 1 gram of polymer in100 ml solvent at at 25.00±0.05° C. The viscosity number was measured ata concentration of 0.5 gram of polymer in 100 ml of solvent at25.00±0.05 ° C. The solvent for the semi aromatic polyamides PA-1 toPA-4 was sulphuric acid 96.00±0.15% m/m, for PA-5 (polyamide 6) thesolvent was 90 wt. % formic acid. The flow time of the solution (t) andthe solvent (to) were measured using a DIN-Ubbelohde from Schott (ref.no. 53020) at 25° C. The relative viscosity is defined as RV=t/t0. Theviscosity number was calculated as follows:

${VN} = {\frac{\left( {\frac{t}{t_{0}} - 1} \right)}{c} = {\left( {\frac{t}{t_{0}} - 1} \right)*200}}$

Wherein:

-   -   VN=viscosity number (mL/g)    -   t=average flow time of the sample solution, in seconds    -   t₀=average flow time of the solvent, in seconds    -   c=concentration, g/mL (=0,005)

DSC Measurements: Tg, Tm and Melting Enthalpy

The melting temperature (Tm) was measured according to ASTM D3418-03 byDSC in the second heating run with a heating rate of 10° C./min.

The melting enthalpy was measured according to ASTM D3418-03 by DSC inthe second heating run with a heating rate of 10° C./min.

The glass transition temperature (Tg) was measured according to ASTM E1356-91 by DSC in the second heating run with a heating rate of 10°C./min, falling in the glass transition range and showing the highestglass transition rate.

Optical Properties

The optical properties were measured according to ASTM D1003A, using aBYK Gardner XL 211 Hazeguard System comprising a halogen light source C.The sensing unit comprised an integrated sphere to collect light that isscattered by a specimen. The collected light was then measured with asilicon photo detector. The specimen was placed at the entrance port formeasurement of haze and/or transmittance. The test specimens used had across section of 50 mm.

The light transmittance is the percentage of the luminous fluxtransmitted through a specimen compared to the luminous flux incidentupon it.

Haze is the percentage of transmitted light passing through a specimenby forward scattering, which deviates from the incident light by no morethan 2.5°.

Processing

Polyamide films were prepared by a film cast extrusion process. A singlescrew extruder (screw diameter 30 mm, L/D=30) was connected to a feedblock with a slot die with adjustable die-lip. The length of the slotdie was 300 mm and the die-width was 0.8 mm. The extruder was fed withthe polyamide material. The film was taken up by and cooled on a chillrole. The thickness of the film was regulated by the chill role windingspeed, thereby affecting the drawdown ratio between the chill rolewinding speed and the extrusion speed. The extrusion speed was keptconstant and was such that with a draw-down ratio of 14, the totalthickness of the film was approximately 50 μm.

All films as described in the examples below were packed in alumina bagsdirectly after production to prevent contact with moisture.

Comparative Experiment A

PA-1 was film processed with a temperature setting of the extrusionzones, feedblock and die of 300° C. The temperature of the chill rolewas 8° C. The distance between die and the position where the filmtouched the chill role was about 1 cm. Film processing was conductedwithout the presence of an air knife. Film thickness was 48 μm. Theoptical quality of the resulting film is quite poor with local whitespots.

EXAMPLE 1

Example 1 was identical to Comparative Experiment A except that an airknife was applied and the temperature of the chill role was 3° C. Thistemperature quench was achieved by cooling of the chill role with icewater. The resulting thickness of the film is 47 μm. The opticproperties of the film, compared to CE-A had improved significantly; nowhite spots were present any more. The optical transparency as judged bythe naked eye was good. The optical transparency measured according tothe method described before was 92.5% (SD 0.1%) and the haze value was2.3% (SD 0.4%).

EXAMPLE 2

Example 2 was identical to example 1 with one difference: the filmthickness was increased to 79 μm by reducing the chill role windingspeed. The optical quality of the film judged by the naked eye was lowercompared to the previous example. The measured optical transparency was92.3% (SD 0.1%) and the haze value was 11.4% (SD 1.0%).

Comparative Experiment B

Comparative Experiment B was identical to example 1 with one difference:the film thickness was increased to 98 μm by reducing the chill rolewinding speed. The optical quality of the film judged by the naked eyewas lower compared to the previous example, the film looked milky. Themeasured optical transparency was 86.3% (SD 0.1%) and the haze value was16.8% (SD 1.0%).

EXAMPLE 3

Example 3 was identical to example 1 with the exception that PA-2 wasused as base material in stead of PA-1. Film thickness was 47 μm. Theoptical transparency as estimated by the naked eye was good. The opticaltransparency measured according to a method described before was 92.5%(SD 0.1%) and the haze value was 1.5% (SD 0.2%).

EXAMPLE 4

In example 4 PA-3 material was film processed with a temperature settingof the extrusion zones of 340° C. and of the feedblock and die of 350°C. The distance between die and the position where the film touched thechill role was between 1 and 1.3 cm. The temperature of the chill rolewas 17° C. The film processing was conducted with the presence of an airknife. The resulting film had a thickness of 48 μm. The optical qualityof the resulting film was good, with a transparency over 92% and a hazeof less than 3%.

Comparative Experiment C

Comparative Experiment C was identical to example 4 with the exceptionof PA-4 material being applied instead of PA-3. The resulting film had athickness of 45 μm. The film appeared to be somewhat hazy and far lesstransparent than the film described in the previous example, the opticaltransparency being less than 88% and the haze being over 12%.

EXAMPLE 5

Example 5 was identical to example 4, except that a blend of PA-3 withPA-5, ratio 80/20, was used. The resulting film had a thickness of 48 μmand the optical quality was good.

Comparative Experiment D

Comparative Experiment D was identical to example 4 with the exceptionof PA-5 material being applied instead of PA-3, and the temperaturesetting of extrusion zones, feedblock and die were adjusted to 250° C.The resulting film had a thickness of 47 μm and the optical quality wasgood.

Further Measurements and Tests

All films as described in the above examples were packed in alumina bagsdirect after production to prevent contact with moisture.

DSC Study

Some of the above films, examples 1,3 and 4, were studied by DSC, tolearn about the crystallinity and crystallization behaviour of thesefilms. Samples of the films were taken from alumina bags and directlyafterwards measured by DSC.

The thermograms as obtained by the first heating curve are discussed.The film of example 4 exhibited a considerable cold crystallization peakafter passing the glass transition temperature, which is considered tobe indicative that the film material was highly amorphous after filmproduction. The melting temperature was 320° C., with a correspondingmelting enthalpy of 64 J/g. After cooling down the sample from the meltby 10° C./min to below room temperature and exposition of the sample toa second heating run with a heating rate of 10° C./min, no indicationswere found for a cold crystallization process. This indicates that thefilm as obtained from the film production process has an amorphouscharacter, which could explain for its high transparency. However, uponannealing of the film, the film kept its transparent character, despitethe crystallization induced by the annealing and evidenced by DSC.

The DSC thermograms of the film samples of examples 1 and 3 showed adifferent behavior, compared to example 4. No indications for coldcrystallization between the glass transition temperature and the meltingpoint were observed, indicating that the films had developed a stablecrystalline morphology during film production. Together with the factthat the films are optical transparent, the interpretation could be thatthe crystallites present, if any, could be very small, smaller than thetypical wavelength of light. The melting temperature of the PA46 filmfrom example 1 was 282° C. with a melting enthalpy of 79 J/g. Themelting temperature of the PA46 film from example 3 was 289° C. with amelting enthalpy of 85 J/g.

Annealing and Water Uptake

Water uptake of the film of example 1 was measured by thermogravimetricanalysis. A microbalance was used in combination with an atmosphere withvarying relative humidity. A film sample was brought in the microbalanceand conditioned in a dry atmosphere to guarantee the film was dry at thestart of the experiment. The sample was exposed to an atmosphere of 85%relative humidity at 85° C.the weight increase due to water uptake ofthe film was monitored. The water uptake of the film of example 1 was6.8 wt %. A series of experiments was performed on film samples that hadbeen thermally annealed in an oven under nitrogen stream at 260° C.before studying the water uptake. The annealing time was varied. Anannealing time of 8 hrs resulted in a lowering of the water uptake from6.8 wt % to 5.2 wt % at 85% relative humidity. Increasing the thermalannealing time to 24 hours resulted in a reduced water uptake of 4.6 wt%. Further increasing the annealing time to 84 hrs resulted in an evenlower water uptake of 1.7 wt %. It was visually observed that the filmsretained their transparency, both after annealing and after thesubsequent water absorption.

Stretching Experiments

Biaxial film stretching experiments were performed on PA46 films. Theseexperiments were performed in a tentaframe device positioned in an oven.The films with areal dimensions of 10 cm* 10 cm were clamped at thesides in this device. The stretching was performed on films taken fromthe alumina bags, clamped and consequently heated by hot air to thestretching temperature.

In a first stretching experiment, the film from Comparative Experiment Awas stretched at a temperature of 100° C. The stretching process was nothomogeneous distributed over the film. The film responded in a veryheterogeneous manner. Rupture occurred at a stretching ratio ofapproximately 1.4 * 1.4.

In a second experiment, the film as prepared in example 2 was stretchedat a temperature of 100° C. The stretching process was ratherhomogeneous and resulted in a transparent stretched film. Maximumstretching ratio before rupture occurred was approximately 2.0 * 2.0.

In a third experiment, the film from example 3 was allowed to swell in awater bath overnight. This film was stretched at room temperature andthe maximum stretching ratio was 2.2 * 2.2. Film stretching occurred ina homogeneous manner. The film was heated to 120° C. and stretched in asecond step to a total overall degree of stretching of 3.0 * 3.0. Theresulting film appeared homogeneous and was transparent.

Oxygen Permeability Test

Films of examples 4 and 5 and Comparative Experiment D were subjected toan oxygen permeability test and the observed permeability for examples 4and 5 was normalized against that of Comparative Experiment D. Comparedto the normalized value of 1 for Comparative Experiment D, the films ofexamples 4 and 5 had a much lower oxygen permeability, which differedonly slightly from each other: 0.25 against 0.26. Apparently thesemi-crystalline polyamide PA-3 in example 4 showed a much lower oxygenpermeability than the aliphatic polyamide PA-6 in Comparative ExperimentD. Despite the presence of 20 wt. % PA-5 in the blend of example 5, thelow oxygen permeability of PA-3 was hardly affected, at least in muchlower extend than could be anticipated on a weight basis.

1. Optically transparent polymer film or extrudate product made of apolymer composition comprising a semi-crystalline polyamide (A) whereinthe semi-crystalline polyamide (A) has a melting temperature (Tm-A) ofat least 270° C. and is present in an amount of respectively at least 60wt. % in case the semi-crystalline polyamide (A) consists of asemi-aromatic semi-crystalline polyamide or of a blend of asemi-aromatic semi-crystalline polyamide and an aliphaticsemi-crystalline polyamide, or at least 75 wt. % the case thesemi-crystalline polyamide (A) consists of an aliphatic semi-crystallinepolyamide, wherein the wt. % is relative to the total weight of thepolymer composition, the polymer composition has a melting temperature(Tm-C) of at least 270° C., and the film or a part of the extrudateproduct has a haze of less than 12% and a light transmittance of atleast 88%, measured with the method according to ASTM D1003A.
 2. Film orproduct according to claim 1, wherein the polymer composition has amelting enthalpy, of at least 25 J/g, measured according to ASTMD3418-03 by DSC in the second heating run with a heating rate of 10°C./min.
 3. Film or product according to claim 1, wherein thesemi-crystalline polyamide (A) is a semi-crystalline semi-aromaticcopolyamide comprising repeat units derived from: (a) 25-45 mole %terephthalic acid, (b) 5-25 mole % of an aromatic dicarboxylic aciddifferent from terephthalic acid, and/or an aliphatic dicarboxylic acid,(c) 5-30 mole % of an diamine chosen from the group consisting ofethylene diamine, trimethylene diamine, tetramethylene diamine andpentamethylene diamine, (d) 20-45% of a diamine comprising at least 6C-atoms, and optionally (e) 0-10 mole % of one or more aminocarboxylicacids and or lactams (f) 0-3 mole % of compounds being mono-functionalor tri-functional in amino and/or carboxylic acid groups; wherein themole % of each of a-f is relative to the total of a-f.
 4. Film orproduct according to claim 1, wherein the semi-crystalline polyamide (A)is polytetramethylene adipamide, or a copolyamide thereof, comprising(i) repeat units derived form tetramethylene diamine and adipic acid and(ii) repeat units derived from other diacids, diamines and/or aminocarboxylic acids and/or lactams, wherein the repeat units (i) derivedfrom tetramethylene adipamide are present in an amount of at least 75wt. %, relative to the total weight of the copolyamide.
 5. Film orproduct according to claim 1, wherein the polymer composition comprisesat least one other polymer and/or at least one additive.
 6. Film orproduct according to claim 1, wherein the polymer composition comprisesan amorphous semi-aromatic polyamide and/or a semi-crystalline aliphaticor semi-aromatic polyamide having a melting temperature below 270° C. 7.Film or product according to claim 1, wherein the polymer compositionconsists of (A) 60-100 wt. % of the semi-crystalline polyamide, (B) 0-40wt. % of at least one other polymer (C) 0-10 wt. % of the at least oneadditive wherein the wt. % are relative to the total weight of thepolymer composition.
 8. Film or product according to claim 1, whereinthe film or a part of the product has a thickness of at most 500 μm. 9.Film or product according to claim 1, wherein the film or a part of theproduct has a haze of less than 5% and a light transmittance of at least90% when measured according to ASTM D1003A.
 10. Process for preparing atransparent polymer film, comprising steps wherein (1) a polymercomposition as according to claim 1 is heated and melt-extruded througha slit die to form an extruded polymer layer; (2) the extruded polymerlayer is led over a chilling role having a temperature below 40° C.,thereby forming a polymer film, and (3) the polymer film is collected,wherein the polymer film has a haze of less than 12% and a lighttransmittance of at least 88% when measured according to ASTM D1003A.11. Process according to claim 10, wherein the slit die and the chillingrole are separated from each other by a distance of at most 1.3 cm andthe chilling role has a surface temperature of at most 8° C., morepreferably the chilling role is cooled with ice water.
 12. Process forafter-treatment of a polymer film, wherein a transparent polymer filmaccording to claim 1 is subjected to a drawing step wherein the film isstretched, and/or a heat setting and/or an annealing step, whereintransparent polymer film, having a glass transition temperature (Tg) anda melting temperature (Tm), is heated to or kept for a certain period ata temperature between the Tg and Tm.
 13. Process for preparing anextrudate product comprising steps wherein i. a polymer composition asaccording to claim 1 is melt extruded through a die; ii. the extrudedpolymer composition is led through a quenching liquid having atemperature below 40° C., thereby forming a solid product, and iii. thesolid product is collected, wherein the solid product comprises a parthaving a haze of less than 12% and a light transmittance of at least 88%when measured according to ASTM D1003A.
 14. Steam-sterilizable medicalarticle comprising an extrudate product according to claim
 1. 15.Packaging materials or electrical or electronic components comprising atransparent polymer film according to claim 1.